MAC1700 Issues

[ulyssewang]

Ulysse
Ulysse
Active Member
I have a MAC 1700 that I partially recapped except the big filter caps and multi caps. It has two minor issues: slight 120hz buzz that can be heard near the receiver and through speakers; static like noise from one channel when turns on, then becomes intermittent, gradually dies down and goes away after one or two hours of running.

I plan to fix these during the break. What are some areas I should start with? I am thinking deoxit all pots again, clean tube pins and seats, fresh heat compound, maybe new filter caps.

I also heard some bias transistors might be the issue for scratchy noise. And I bought some replacement parts. But I find it really hard to remove the original ones, as legs are soldered through small tubes. Any advice on how to desolder these?

Anything else might be the culprit?

Thanks!

 

[sgrossklass]

I have a MAC 1700 that I partially recapped except the big filter caps and multi caps. It has two minor issues: slight 120hz buzz that can be heard near the receiver and through speakers; static like noise from one channel when turns on, then becomes intermittent, gradually dies down and goes away after one or two hours of running.

The static problem very much sounds like a bad electrolytic specific to this channel.

Hum at unit itself is generally mechanical in nature. Make sure the transformer is fastened properly, that's generally all you can do.

Hum through speakers may indicate that some filter caps have seen better days, but also inherent construction issues.

Looks like the MAC1700 is a roughly 50-year-old McIntosh receiver? I definitely wouldn't be surprised to find shot filter caps in a unit this old.

 

[ulyssewang]

I changed the big filter caps. Now the hum seems gone. However, still has some static/scratchy noise intermittently on the same channel, but much better than before.